<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<style>
.main {
    background-color: #aaa;
    width: 90%;
    height: 500px;
    margin: 0 auto;
}
</style>

<body>
    <div class="main"></div>
</body>

</html>
